The objective of this project is to investigate the regulation of 2 key morphogenetic events during mouse preimplantation development, which are compaction and the morula-to-blastocyst transformation. These 2 events are accompanied by, and may depend on, the expression of certain cell surface antigens and are inhibited by drugs that disrupt cytoskeletal elements (microfilaments and microtubules), two observations that are consistent with the hypothesis that cell surface-cytoskeletal relationships are involved in morphogenetic events. The specific aims are, therefore: 1. to define the transmembrane relationships between cell surface antigens and cytoskeletal elements by using drugs that perturb cytoskeletal elements together with the immunolabelling of these antigens with the appropriate antisera. These exxeriments will be monitored by indirect immunofluorescence and by immunoelectron microscopy. 2. to relate these relationships to compaction and the morula-to-blastocyst transformation by comparing cell surface antigen-cytoskeletal relationships in normal embryos with those in embryos that have ceased to develop because they were cultured in dilutions of these antisera, which can reversibly inhibit development as these morhogenetic events are taking place. This approach will allow, for the first time, a direct analysis of how specific morphogenetic processes are related to specific examples of cell surface cytoskeletal interactions, and has the potential of generating a unified concept of how morphogenetic processes are regulated during early mammalian development.